The following correction was printed in the Guardian's Corrections and clarifications column, Tuesday March 13 2007 The world wide web and not the internet was born in the Cern laboratories. The internet began as a US military project that connected different and distant computer networks. The web is an application which allows users to navigate within and between documents using internal connections, or hyperlinks. When the ancient Greek historian Herodotus was about four years old, a tiny army of 300 Spartans, 700 Thespians and a small cluster of Greek allies fought one of the most famous battles in history: Thermopylae. Here, at the "hot gates", a mountain pass in central Greece, the unprecedented Persian army of Xerxes I (estimated by Herodotus to number 2.6 million, excluding elephants and horses) was held back long enough for the Greeks to prepare a counterattack by land and sea that would trounce Xerxes and spare western civilisation from being overrun from the feared east.

The battle had been a true wonder, and even though every one of Leonidas's men was killed, the Greeks had every right to be elated, and in myth-making mood. In adult life, Herodotus drew up a list of seven wonders of the world, although we only know about this through passing references.

So too, some 200 years later, did Callimachus of Cyrene - a librarian at the Museum of Alexandria that later became the Royal Library, a wonder itself.

Who knows how many lists were drawn up over the centuries, but long after Greece had been annexed by Rome and Rome itself had declined and fallen, the seven wonders of the world had become an established and familiar part of western mythology.

Until, perhaps, Greek and then Latin began to disappear from school curriculums in recent years, millions of children could reel off this list of primarily Greek achievements. The statue of Zeus at Olympia, where the first Olympic games had been held in 776BC; the Colossus of Rhodes; the Mausoleum in Herodotus's home town, Halicarnassus; the Lighthouse of Alexandria; the Temple of Artemis at Ephesus (destroyed by a Christian mob led by St John Chrysostom in 401AD, with parts of its 12-metre marble columns reused in a later architectural wonder, the Hagia Sophia in Constantinople); the Hanging Gardens of Babylon, and the Great Pyramid of Giza, the only one of the seven ancient wonders still standing.

National myths

Herodotus might just have visited all seven (he seems to have been to Egypt, if not to Mesopotamia); yet, whether he did or not, the wonders would have been tourists attractions of the Roman era; the Greeks themselves called them theamata, which roughly translates in today's terms as "must-sees"; so here were seven attractions you had to see before you died, or your empire fell.

Herodotus claimed that the Hanging Gardens of Babylon grew along 56 miles of walls surrounding Nebuchadnezzar II's city (rebuilt in part by Saddam Hussein). They were, he said, 25 metres thick and nearly 100 metres high. Reports of the scale and extent of the Gardens were perhaps greatly exaggerated. As for the Colossus of Rhodes, a huge statue of the sun god Helios, although it may have been the same size as the Statue of Liberty, it did not straddle the harbour mouth at Rhodes, even though this is how it has been depicted time and again over the centuries.

The wonders were always more than real places, artworks and buildings. They were about national pride and mythology; they fed the imagination of millions of people over many centuries who would never have had even the hint of a chance of visiting one of them.

And, because they were mythic, they had to be part of a magic number. Three wonders of the world would have been too few to haunt the imagination. Twenty would be too many. Seven was satisfyingly right. For the Greeks, as with civilisations around the globe, the number seven has special, arcane, magical and even divine properties.

Perhaps of particular significance to the Greeks was the fact that there were seven wonders of the heavens to be seen from the Earth with the naked eye: the Sun, Moon, Mercury, Mars, Venus, Jupiter and Saturn. These celestial bodies gave their names to the most important classical gods, as well as to the seven days of the week. Perhaps, then, (and especially in such a clearly gifted and fortunate civilisation), there must have been seven man-made wonders worthy of celebration and myth-making too.

Today, when we have become inured by a never ending supply of attenuated media lists, the Greek seven is both happily taut, and retains the power to excite the imagination. What were those Hanging Gardens like? How colossal was the Colossus of Rhodes? Could the light from the Lighthouse of Alexandria really been seen by ships 35 miles from shore?

And, yet, over the centuries, as the idea has continued to invade the collective imagination, as more "wonders", or "must-sees" have been shaped, and as ever more people have found a voice of their own, it has been ever harder to pin down a properly satisfying and universally acknowledged list of just seven.

The Middle Ages had their own fascination with such epic monuments as the Tower of Babel, the Temple of Jerusalem and the Roman Colosseum. Individual nations and local cultures were possessive of the legendary power of structures in their own backyards: Stonehenge, Hadrian's Villa, the Great Wall of China.

In the age of mass travel and the internet that has followed an earlier era of insatiable exploration and archaeology, the number of "must sees" has grown.

On July 7th this year - 07/07/07 - a "New Seven Wonders of the World Declaration" will be made in Lisbon. The brainchild of Bernard Weber, a Swiss-born American film producer, pilot and author, the event will celebrate seven wonders as voted for by millions of people worldwide.

Weber's shortlist of 21 wonders is remarkably conservative. The pyramids of Giza are there (all three, rather than just the big one), as is the Great Wall of China, Stonehenge and the Colosseum. Among the others are the Taj Mahal, Sydney Opera House, Chichén Itzá, the Kremlin, Neuschwanstein and Timbuktu. While each of these is fascinating and endearing in its own right, it is hard not to think that Weber's 21 are there to please everyone, and, as you might say, just a touch geographically correct.

Modern wonders might be different things from heroic constructions of marble, stone and steel. My own list would include the first colour photograph of Earth taken from space, from Apollo 8 in 1968. Here was a defining moment in our collective psyche. Not only was the Earth itself revealed, without a shadow of a religious doubt, to be a wonder in itself, it was also evidently a wonder to be cherished.

Crick and Watson's model of the DNA double helix is another wonder of our times, as is the soon-to-be-fired-up giant particle accelerator at Cern on the Franco-Swiss border. Here is a machine that will do its best to replicate conditions at the exact moment of the big bang. It was also in the Cern laboratories that the internet was born, an invisible wonder that has done so much to make events such as those planned in Lisbon on 07/07/07 possible.

From the big bang, through the structural magnificence of the Great Pyramid of Cheops, through heroic engineering structures from the Forth railway bridge to Concorde, and on to the infinite ways of the internet, wonders will never cease.